1. Field of the Invention
This invention relates to the production of hydroperoxides of hydrocarbons having no aliphatic or cycloaliphatic tertiary carbon atoms and more particularly it relates to the production of the hydroperoxides by oxidation of such hydrocarbons in the liquid phase with molecular oxygen as the oxidizing agent.
2. Prior Art
It is well-known from the published technical and patent literature that the oxidation of hydrocarbons having tertiary carbon atoms such as isobutane, cumene, p-cymene, and the like to the corresponding hydroperoxide using molecular oxygen is commercially feasible. High selectivities at high conversions and conversion rates are readily obtainable.
The oxidation of hydrocarbons which do not have a tertiary carbon atom such as cyclohexane, ethylbenzene and the like to the corresponding hydroperoxide using molecular oxygen is not commercially feasible, since only at very low conversions and conversion rates is it possible to obtain a reasonably high selectivity for the hydroperoxide, i.e., about 50 percent.
These findings are explained by the fact that the tertiary carbon-hydrogen bond is the weakest bond in the compounds containing a tertiary carbon and accordingly, this bond is attacked readily in the oxidation reaction giving a high rate of conversion and producing a tertiary hydroperoxide which is quite stable. This permits the reaction to be carried out to a high conversion level of the hydrocarbon while at the same time the selectivity to the hydroperoxide is very good. Only small amounts of acidic and high boiling residue is produced. This is not true for the oxidation of hydrocarbons having no aliphatic or cycloaliphatic tertiary carbon atoms, e.g., those having aliphatic or cycloaliphatic secondary carbon-hydrogen bonds. The rate of conversion is much slower because of the increased bond strength of the secondary carbon-hydrogen bond and the oxidation must be carried out at low conversion of the hydrocarbon to obtain high yields of the hydroperoxide, which moreover, is considerably less stable than the tertiary hydroperoxides. If it is attempted to carry out the oxidation at high conversions large amounts of high boiling residues are produced since competing side reactions occur.
The literature shows, for example, that the total conversion in the oxidation of cyclohexane cannot be above about 1.5 - 2 percent if a 50 percent yield of the hydroperoxide is desired. At a 4 per cent conversion the maximum yield of the hydroperoxide is only about 30 per cent. Heretofore, various proposals have been made to circumvent these disadvantages, for example, aluminum reactors, low rates of conversion, low total conversion of hydrocarbon alone or concurrently with the removal of by-product acids. Although these proposals have indicated that acceptable yields of hydroperoxide can be obtained by their use, none are economically or commercially feasible.
In a co-pending application it is proposed to add to the reaction medium stabilizers for the hydroperoxide such as tertiary butyl alcohol, water or an aqueous buffer solution. This proposal gives high selectivities for the hydroperoxide even at conversions of the hydrocarbon of 8 per cent or more. This proposal which is a marked improvement over the prior art did not completely obviate all of the difficulties, since conversion rates were still relatively low, i.e., of the order of 2 per cent per hour. The present invention provides an additional improvement in that relatively high conversion rates are obtainable in addition to the high conversion and selectivity. This is accomplished by introducing both a tertiary alcohol and a tertiary hydroperoxide into the reaction zone together with the hydrocarbon feed and the molecular oxygen oxidizing agent.